Vehicles are often driven very short distances with the engine running for short periods of time as the vehicles are moved to various temporary storage locations during vehicle assembly. Vehicles may be stored inside or outside for various periods of time before they are loaded on rail cars for transportation to dealerships for delivery to customers. These short engine start and restart cycles under various ambient conditions may lead to formation of carbon and other deposits on one or more spark plugs that could ultimately result in plug fouling and undesirable engine performance. One strategy used to prevent plug fouling associated with short run times at the assembly plant employs an alternate engine calibration with a lean air/fuel ratio, advanced spark timing, and elevated engine idle speed to develop more heat in the combustion chambers and eliminate any spark plug deposits. The alternate calibration affects all cylinders on every start. While this strategy generally reduces or prevents formation of spark plug deposits, the lean air/fuel ratio of the alternate calibration may result in engine stalling, particularly for cold starts, and the higher engine idle speed may be objectionable to some customers. As such, the alternate calibration is employed only for a limited number of engine starts and/or a maximum mileage driven in a single trip so that it is no longer active by the time the vehicle is delivered to a customer. The engine/vehicle controller then uses the regular production calibration and the alternate calibration is never accessed again. However, some customers may have operate the vehicle under similar conditions with short drive cycles that facilitate spark plug deposit formation and could benefit from a similar control strategy to reduce or eliminate plug fouling.
To improve control of the combustion process, ionization current sensing (or ion sense) uses a bias voltage applied across a sensor positioned within the combustion chamber to generate a current signal indicative of the combustion quality and timing. The ion current signal may be used to provide early detection of plug fouling with various corrective actions, as described in U.S. Pat. No. 7,302,932, for example. Depending on the particular engine technology and detected condition, the ion current signal may be used to adjust ignition timing, valve timing, fueling, and/or airflow, for example, to better manage the combustion process.